Development of an Axial Fractionator for Hemp Shive Cleaning and

Development of an Axial Fractionator for Hemp Shive Cleaning and

Journal of Agricultural Science; Vol. 5, No. 1; 2013
ISSN 1916-9752 E-ISSN 1916-9760
Published by Canadian Center of Science and Education
Development of an Axial Fractionator for Hemp Shive Cleaning and
Industrial Applications of Shives
Carsten Lühr1, Ralf Pecenka1, Hans-Jörg Gusovius1, Gesine Wallot1, Roman Rinberg2 & Sören Tech3
1
Department of Post Harvest Technology, Leibniz Institute for Agricultural Engineering Potsdam-Bornim,
Germany
2
Composite lightweight construction and polymer processing, Chemnitz University of Technology, Germany
3
Wood and Paper Technology, Technical University Dresden, Germany
Correspondence: Carsten Lühr, Department of Post Harvest Technology, Leibniz Institute for Agricultural
Engineering Potsdam-Bornim, Germany. E-mail: [email protected]
Received: September 17, 2012
doi:10.5539/jas.v5n1p9
Accepted: October 9, 2012
Online Published: December 13, 2012
URL: http://dx.doi.org/10.5539/jas.v5n1p9
Abstract
Due to increasing shortage of raw materials, traditionally used for production of wood based panels and other
composite materials, there is a growing call for the use of raw materials from agricultural production. Hemp
shive, a by-product of hemp straw processing, is in eager demand due to its wood-like material properties. In
order to be suitable for industrial use, respective agricultural raw material must be competitive in price, as well
as be available in respective quantity and quality. ATB has developed a new processing technology for the
cleaning of shive-fibre mixes for better accommodation such requirements. Ultimate goal is the generation of
dust and fibre free shives as well as the recovering of high quality short fibres from shive fractionation.
This is facilitated by a new type of axial fractionators, which utilizes a multi-stage paddle screw and a screen
drum, corresponding with the screw. This allows classification and cleaning of the shives as well as recovering
of the short fibres in only one processing step. Finished products are widely dust and fibre-free, high value
shives; and shive-free short fibres. The shives can be used for the production of particle boards without further
preparation. The recovered short fibres are mainly suitable for the use as reinforcing fibres in composite
materials due to their short fibre length (<50 mm).
In cooperation with a machine engineering company, the design of the developed axial fractionator shall be
adapted for industrial application. Owed to its simple and flexible design, common by-products of hemp
processing can be processed at reasonable costs into high-quality market-going products.
1. Introduction
For a considerable period of time, growing shortage and a cost increase of raw materials for the wood based
panel and composites industry has been evident. The use of wood as a fuel additionally boosts the demand in
cellulose raw materials (Pecenka et al., 2010). Wood-like raw materials, e.g. from agricultural production, can be
understood as alternative or supplement to the classical range of raw materials. Besides cereal straw, hemp and
flax could play an important role as wood substitute in future. Some of the biggest hemp producers are Europe
(approx. 8,000 ha/year 2011), Canada (approx. 16,000 ha/year 2011) and China (more than 80,000 ha/year 2008)
(Kruse, 2012; Müssig, 2010). Especially in Canada hemp is mainly cultivated for seed production. Therefore, the
straw could be used at reduced raw material costs for industrial applications if adequate processing technologies
are available. Furthermore, in year 2012 more than 430,000 ha of flax have been cultivated for seed production
in Canada alone (Agriculture and Agri-Food Canada, 2012). Because modern processing facilities for bast fibre
production are able to process hemp and flax with the same equipment, an interesting additional income for
farmers could be generated from flax straw.
A large proportion of the produced natural fibre from hemp and flax is used for the production of insulation
material and fibre fleeces. Substitution of synthetic fibres (e.g. glass fibre) in composite materials by natural
fibres, yet maintaining similar properties of the composite, is also considered feasible (Graupner & Müssig,
2009). Natural fibres and glass fibres show comparable specific strengths and Young's moduli (Bledzki, Gassan,
Fink, & Kleinholz, 1999). The demand for shive, which at 50-60 mass-% make up for the significantly larger
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Vol. 5, No. 1; 2013
proportionn compared to the fibre in hemp
h
straw (F
FNR, 2008), is
i well nurtureed by a stablee market of annimal
bedding materials
m
for ppets and horsses. Besides tthat, cleaned, high quality shives for particle
p
boardss are
increasingly interesting aas partial or co
omplete substittution for shavvings in the wo
ood based paneel industry.
This, howeever, requires an efficient clleaning technoology for hempp shives. The high quality requirements
r
oof the
wood baseed panel and composites in
ndustry regardding shives annd fibres coulld only be meet, if fibre caan be
effectivelyy recovered froom the mix, an
nd shives are clleaned properly from dust.
In recent years, intensiive research has
h been donne in the devvelopment of efficient techhnologies for fibre
decorticatiion (Munder, F
Fürll, & Hemp
pel, 2004; Peccenka, Fürll, Gusovius,
G
& Hoffmann,
H
20009) as well as fibre
and shive cleaning (Peceenka, 2008; Fü
ürll, Pecenka, & Bojdzinski, 2008), at the Leibniz Instituute for Agriculltural
Engineerinng Potsdam-Bornim (ATB). As a result oof researching different proccesses for shivve cleaning, a new
variant waas developed; rregistered for patent
p
(Fürll, P
Pecenka, & Boojdzinski, 2010); and successsfully tested uunder
lab conditiions (Fürll et aal., 2008). For further develoopment of this process, a testt plant for the processing
p
of uup to
1.5 t/h shiive-fibre mix w
was build, wh
hich is currentlly tested undeer industrial co
onditions in a fibre decortication
plant and further
f
developped to practicee application.
2. Industrrial Condition
ns in Fibre Decortication
Figure 1 shhows a schem
matic drawing of
o the fibre deccortication plaant developed in
i cooperationn with the ATB
B and
currently used
u
in practicce test operatio
on. Normally, in high capaccity fibre decorrtication plantss, hammer millls or
sifter millss are used forr the decortication of straw - the core proocess of the ov
verall processiing (Munder eet al.,
2004)-(stage 4). Here the actual decorttication takes pplace, i.e. the mechanical seeparation of shhive and fibres.. The
shive is thhe milled parrt of the ligneous core of the hemp strraw. In order to process thhe hemp straaw in
continuoussly good qualitty at high plan
nt flow rates, itt must be shorttened prior pro
ocessing using a cutting macchine.
The hemp straw is then evenly and lo
oosely suppliedd to the hamm
mer mill via a hopper. Subseequently, the ffibres
are cleanedd, whereby diffferent shive-ffibre mixes acccumulate as byy-products. Th
he shives have to be cleaned from
dust, and the
t fibres contaained in the miix must be recovered, if posssible.
Figgure 1. Schem
matic drawing oof an industriall fibre decorticcation plant
3. Curren
nt Situation in Shive Processsing
The decorttified fibre conntent in hemp straw -dependdent on the typpe of straw and
d growing condditions- is at cca. 30
mass-% (F
Francken-Welzz & Léon, 200
03; Höppner & Menge-Hartm
mann, 2000). This,
T
however, means that ca. 70
mass-% off by-products w
will accumulaate on fibre prooduction. A laarge proportion
n of these by-pproducts are shhives
and fibre mixes (Figurre 2). For thee efficient opperation of a fibre decorticcation plant thhese accumulating
by-products must be processed in ways that can be m
marketed effecttively.
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Journal of A
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Dust
Fibrres
Vol. 5, No. 1; 2013
Discharrge of decortication
Shive
e-fibre mix
15%
%
45%
29%
11%
%
Figure 2. Mass ratio of accumulating by-products inn fibre producttion of hemp sttraw
(for reetted hemp straaw at a mass flow
f
of 1.1 t/h))
The goal is
i to develop a flexible fracctionator and ccleaning plantt for shive-fibrre mixes for the
t processing of a
large range of different straw types, based on the prrinciple of an axial
a
fractionaator examined at ATB. The llatter
has to accoommodate a m
mass flow of 2 t/h, matchingg a plant mass flow of ca. 4 t/h hemp straw
w. This straw mass
flow can cater
c
for efficcient fibre pro
oduction (Peceenka et al., 20009). During this
t
process, the
t shives shaall be
cleaned frrom dust and short fibres with
w a mass coontent in shives of less than
n 6 mass-% shall
s
be recovvered.
Additionallly, ultra short fibres (5-20 mm
m length) conntained in the mix, shall be separated and made availablle for
industrial use
u as reinforccing fibres, e.g
g. in injection m
moulding.
4. Materiaal and Method
ds
The compoosition of the shive-fibre miix to be cleaneed (Figure 3) depends
d
on thee retting degreee of the used hhemp
straw. Diffferent straw ttypes require an
a adaptation of the operattion parameterrs in a fibre decortication
d
pplant,
which resuults in modificcations of the composition
c
off the shive-fibrre mix. Generaally, the mix consists of the main
componennts dust, shivess, and short fib
bres. The mainn problem for effective clean
ning of the mix is that the shhives
are entanggled and partiially enclosed in the fibre flakes. This form
f
closure between the fibres preventts an
unhinderedd drop out of tthe shives. Furrthermore, therre are shives thhat have no cleean fracture buut still have frayying.
Thereby itt is in this casee a form closu
ure with the fibbres. It should be mentioned
d that an inadeqquate decortication
of hemp sttraw, which is especial noticeable at slightlly retted straw
w, shives are stiill firmly bounnd to the fibress by a
force closuure.
100
Mass ratio [%]
Fibres
80
> 8.0 mm
>4.0-8.0 mm
m
60
>2.0-4.0 mm
m
40
>1.0-2.5 mm
m
>0.5-1.0 mm
m
20
0-0.5 mm
0
slightly
retted
rette
ed
a)
retted
b)
Straw type
reetted
c)
strongly
retted
Figure 3. Shive-fibre m
mix as accumulated by-producct of fibre prodduction, and mass
m ratio of sccreen fractionaation
for diffeerent straw typpes
It is thus not
n possible to separate the mix
m to a sufficiient degree witth the usual claassing technologies. Since shhives
and fibres are very lightt weight and feature
f
similarr lifting speedds there is a laack of driving weight force for a
separation (elimination/eexcess of bindiing forces betw
ween shive andd fibres). Only
y active, mechaanical intervenntion,
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Journal of Agricultural Science
Vol. 5, No. 1; 2013
as realized in the axial fractionator (Figure 4), can accommodate a reliable separation of the mix into its main
components.
Figure 4. ATB-test plant for cleaning of shive-fibre mixes (axial fractionator)
1) shive-fibre mix; 2) fine shives; 3) rough shives; 4) shives and short fibres; 5) shives and short fibres; 6) cleaned
short fibres
The plant consists of two cleaning stages, featuring the paddle screw principle. The movement paths of the
particles at the paddle as well as the respective material flows are schematically shown in Figure 5. Three different
movement types, facilitating effective separation of the shive-fibre mix, can be realized dependent on parameters
like paddle form, paddle pitch, and circumferential speed.
Figure 5. Material flow and straining process of a shive-fibre mix in the axial fractionator
a) flow over the paddle; b) flow along the paddle; c) dropping from paddle.
On the one hand, as in material flow a) the mix flows over the paddle and the newly aligned shives can pass
through the cleared screen behind the paddle. On the other hand, as in material flow b) the mix is moved forward
over the screen by pitching the paddle axially, thus causing the shives to pass through the screen as well. By
dropping the flake from the paddle, as in material flow c) and simultaneously crushing the fibre flake by a
successive paddle, the shives are threshed from the flake and can thus pass through the screen.
5. Results
Figure 6 shows selected fractionation examples, generated by cleaning of shive-fibre mixes in an axial
fractionator. Figure 7 shows the detailed proportionate content of end products from the shive flow, as collected
after the cleaning of the shive-fibre mix in the axial fractionator.
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Figure 6. Sepaarated output ffractionations from
f
axial fracctionator
(lleft to right: du
ust/smallest shives; cleaned shives;
s
recoverred fibres)
Unclean sh
hive-fibremiix
12%
Cleaneed shives
775%
Recovered fiibres
5%
Extraction of dust
and short fibres
2%
Dust / smallest
shives
6%
Figure 7. Fractionations after
a
cleaning iin axial fractioonator (slightly
y retted hemp straw)
s
mass distributioon and thus th
he compositionn of the indivvidual
By variation of suitablee screen mesh widths the m
a
stilll unclean flakke of shive-fib
bre mix makees up the so-ccalled
fractionations can be addjusted. The apparently
excess of processing
p
in the axial fracttionator. It connsists particulaarly of very larrge shives, as well as shivess still
firmly entangled with thhe fibres. Thiss excess can eeither be used for targeted marketing,
m
e.gg. as loose matterial
insulation,, or e.g. redistrributed to the decortication
d
pplant for further milling and complete
c
decortication.
Mass ratio [%]
100
80
60
Fib
bres
40
Sh
hives
20
0
s
strongly
retted
retted
slightly rettted
Straaw type
winter hemp
h
Figuree 8. Compositiion of the recoovered fibre byy using the axiaal fractionatorss
d) are a substaantial factor foor the
The recovered fibres of 5 mass-% (relative to the shhive-fibre mixx to be cleaned
nsidered usual fibre prices), since they make up nearlyy 1/10 of the ffibres
efficiency of the plant ooperation (con
upply such fibrres in market-ggoing
contained in the hemp plant. Currently an additional ccleaning step iss required to su
ximum could not
n yet be achiieved
quality. Thhe required content of shivess in the recoveered fibres of 6 mass-% max
with the teest plant, due too its insufficient dimensions for industrial application (F
Figure 8).
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Journal of Agricultural Science
Vol. 5, No. 1; 2013
Moreover, the currently existing test plant was fitted with a close-meshed screen in the first section of the paddle
screw for the separation of dust and sand particles. The utilization of dust separation via gravitation and the
respective load reduction in the further cleaning process has also proved to be very effective (Figure 9).
Dust / smallest shives (through fraction)
Unclean shives (charging material)
Cleaned shives
Dust / smallest shives (through fraction)
Unclean shives (charging material)
Cleaned shives
Cumulative curve Q3,i (x) [%]
Mass ratio [%]
Cumulative curve Q3,i (x) [%]
Mass ratio [%]
100
80
60
40
Sieve:
Round hole: 1 mm
Free space: 22,7%
20
0
0
0.5
1
2.5
4
Particle size x [mm]
8
11.2
100
80
60
40
Sieve:
Round hole: 2 mm
Free space: 40,0%
20
0
0
0.5
1
2.5
4
Particle size x [mm]
8
11.2
Figure 9. Particle size of cleaned and unclean shives, using different mesh sizes for dust separation in the axial
fractionator (shown without fibre)
By variation of the first screen mesh-width, the composition of the separated dust ratio can be controlled and the
quality of cleaned shives can be adapted to market requirements. The cleaned shives are the largest proportion of
the generated materials and have an insignificant content of dust and short fibre.
The processed shives were recovered to fibre and subsequently pressed to medium density fibre boards (MDF) and
particle boards. Figure 10 shows the compared bending strengths of the boards made from different raw materials
under addition of 10 mass-% of PF-resin.
Bending strength [N/mm²]
25
Particle
board
Fibre boards
20
15
10
Density [kg/m³]
5
600
600
600
600
550
550
600
500
0
Raw material
Figure 10. Bending strength of medium density fibre and particle boards from different raw materials
Due to their high purity, the shives (free of dust and short fibres) could be directly processed to particle boards
(Figure 11).
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Journal of Agricultural Science
Vol. 5, No. 1; 2013
Figure 11. Shive particle board with HPL-surface and 2 mm front liner, shavings completely substituted by
shives
Potential particle board densities, dependent on the shive properties, are currently examined in detail. This is
supplemented by research about the suitability of the separated short fibres and the ultra-short fibres for the use in
injection moulding materials. Current findings allow expectations for production potential of composites based on
these fibres, featuring similar properties as composites produced from conventional hemp fibres. Using these
fibres for injection moulding processes has advantages due to the improved agglomeration properties of the
recovered ultra-short fibres and low costs for raw-material or granulates respectively.
6. Conclusions
Farmers need reliable partners in the processing industry for profitable cropping of bast fibre plants for industrial
applications. Efficient technologies for fibre processing have been developed in the last decade. Additionally, the
implementation of efficient shive cleaning technologies in new processing lines plays an important role for the
overall economy of hemp and flax processing.
The research to the axial fractionator has shown that hemp shives can be effectively cleaned with the developed
plant concept and consequently be used in wood based panels due to their high quality. The manufacturing cost
on the basis of dried chips or shives for producing shive boards are similar to particle boards. The quality hemp
shives as a raw material can be offered for a price from 150 to 180 € t-1. The recovering of short fibres and
ultra-short fibres in the axial fractionator can result in an increased fibre generation for the overall process by up
to 10 mass-% (relative to the fibre content) and thus improve the efficiency of plant operation. Due to the shorter
fibre length of the recovered fibre compared to the conventional technical hemp fibre, they are well suitable for
the use in injection moulding materials. Currently, detailed research is carried out for this application with
respect to processing and product properties compared to conventional reinforcing fibres.
According to experience with the test plant, operated under practice conditions, a reviewed plant concept for
industrial application of a shive cleaning plant has been developed with a machine engineering company.
Advantages of the new axial fractionator will be a simpler design of the screen path, higher mass flow (2 t/h
shive-fibre mix) and relatively higher quality of recovered fibres (rest shive content <6 mass-%).
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